Vapor phase corrosion inhibition



United States Patent VAPOR PHASE CORROSION INHIBITION Philip J. Raifsnider, Richmond, Calif., assignor to Shell Oil Company, a corporation of Delaware No Drawing. Filed June 9, 1959, Ser. No. 819,023

4 Claims. (CI. 21-25) V This invention relates to corrosion inhibition. More particularly, the invention relates to a process of preventing the corrosion of metal articles by the use of wrapping materials, such as cellulosic substances and their derivatives which are coated, impregnated or otherwise contain a particular vapor phase corrosion inhibitor described below.

During storage, handling, transportation and preservation of objects having metal or metal-containing surfaces, especially those of various steels, aluminum, copper and brass, it is often necessary to prevent the corrosion of these metals. Heretoforc, the various methods used for this purpose have involved the employment of relatively expensive vapor phase corrosion inhibitors, such as amine carboxylates or amine nitrites. Additionally, other means which have been employed have included the actual coating of the metals to be preserved with oleaginous compositions containing a wide variety of corrosion inhibitors which are useful only on contact. Under certain conditions, oil compositions have been employed which have contained corrosion inhibitors designed to volatilize from the heat and thereby form a corrosion inhibitor atmosphere above the oil, the atmosphere being confined by an enclosing metallic space, such as a crank case or the like. The disadvantage and limitations of such a system are immediately apparent. In the first place, of course, oleaginous corrosion protective media including such oil compositions require the metal objects so protected to be cleaned prior to their eventual utilization in most cases. Secondly, the presence of oils often masks or diminishes the effectiveness of any corrosion inhibitor present therein. In fact, it is often necessary to activate corrosion inhibitors in lubricating oils by the incorporation of other materials, such as sulfur-containing compounds, phenolic compounds and/or polycarboxylic acids, their amides 0r esters. All of these modifications, of course, increase the cost of the corrosion inhibiting composition and the cost is further increased by the necessity'of removing the oil or oleaginous substance from the metal part prior to its being used.

Partially or completely closed metal parts are usually housed, packaged, boxed, enveloped or placed in a container under such conditions that water vapor and air are either present or introduced to the metal parts at the time of their being exposed therein,- or water'vapor with air enters through the enclosure walls after the packaging.

It is an object of the present invention to obviate the above and other defects, and to provide novel products or materials, which may be used as the enclosing or packaging means per se, or therein, and which materials are capable of inhibiting corrosion of metal parts stored or disposed in such containers or packaging means and/or in said enclosure means containing the novel materials.

Now, in accordance with the present invention, it has been found that capric acid deposited on or incorporated in a substantially solid (preferably fibrous) packaging material acts as a corrosion inhibitor for metal articles wrapped in the material at temperatures between about 30 F. and about 110 F. At higher temperatures, for a reason not determined, the inhibiting effect is lost. This is not accountable by reference to vapor prmsurqsince at 30-110" F. the vapor pressure of capric acid is, of course, lower than it would he, say at F. In further accordance with this invention, it has been found that capric acid not only constitutes a low-priced vapor phase corro-. sion inhibitor as compared with other fatty acids but also.

constitutes the most effective vapor phase corrosion inhibitor for storage and protection of metal parts at ambient temperatures as compared with its immediate homo-, logs. Still in accordance with this invention, the material on which capric acid is deposited or incorporated may be further modified by the presence of an amine car boxylate, preferably the salt of an amine with a fatty acid porous or absorbent or completely impervious substances."

Preferably, the solid material chosen is one which'has a fibrous structure so as to allow for absorption of the capric acid between the individual fibers of the barrier.

where the carrier material is not particularly absorbent, it may advantageously be coated instead of impregnated with the acid.

One of the advantages of the invention comprises the freedom of environment in which the acid is highly effec-; tive as corrosion inhibitor. For example, with many types of vapor phase corrosion inhibitors, it is necessary that the wrapper either be neutral or slightly basic. Such is not the case with capric acid. Moreover, many materials, such as brass or copper, are stained or evencorrodedby' amines. Consequently, amines or amine nitrites are not always satisfactory for the corrosion inhibition of such materials. Capric acid on the other hand has been found to be fully satisfactory for the purpose of inhibiting corro sion of copper-containing metals, in addition to ferrugi nous metals, such as steels or irons.

Representative examples of solid materials which are suitable for use in conjunction with capric acid for'the purpose are paper, textile fabrics, such as cotton, wool or silk, Wood, modified or stiffened paper, such as cardboard, fiber board and laminated papers; synthetic fibers or spun textiles, such as rayons, polyesters, polyamides,'ny lon and polyethylene; asbestos, charcoal, activated char coal, alumina gel and silica gel may be impregnated with capric acid and utilized in conjunction with a wrapping; material. Any sheet or strip material made of the above; fiber substances maybe utilized to prepare the articles of the invention. Impregnation or deposition of the capric acid on any of the above solid materials may be carried out by wetting, immersion, or soaking of the materialwith a dispersion .or solution of capric acid, preferably in a relatively volatile organic solvent. The impregnation. may also be carried out by distributing a.melt.of capric acid, with or without a melting point lowering agentupon the surface of the solid carrier material. The fibrous materials may be impregnated by contact with vapors of the capric acid as well.

In many cases it is advantageous to treat or impregnate one or more layers of a paper laminate with capric acid and then fabricate these into a finished laminated composition which contains outer layers which are much less porous or distinctly less impervious to the vapors of the inhibitor than are the impregnated laminates which may be used for the interior of the package or which are placed close to a corrodible metal. In such cases, the outer laminate may be a metal foil, such as tin or aluminum, preferably of sufiicient thickness that it contains no pin holes.

Thus, capric acid may be incor:

Similar results have been obtained by coating one side of the capric acid impregnated paper with a film of wax.

One of the surprising features of this invention comprises the unexpected difiference found between the action of closely related fatty acids in their vapor phase corrosion inhibition when vaporized from paper or other wrapping material as compared with the action obtained when the acids are dispersed in an oleaginous medium. lnthe latter environment the corrosion protection obtained is substantially the same for a number of difierent fatty acids, little in distinguishing difierences having been found between closely associated homologs of capric acid. However, when the environment is essentially dry, that is, an environment in which essentially no oil or other liquid is present, the vapor phase inhibiting power of capric acid is critical. This is shown in the working examples wherein caproic and caprylic acids as well as lauric acid are compared for their vapor phase inhibiting power with capric acid. As the data show, caproic and caprylic acids actually accelerate rusting while lauric acid (the next even higher homolog of oapric acid) is of only limited effect under the ambient temperature conditions of rusting investigated. Compared with these, capric acid was found to be highly effective for this purpose when the metal being protected was iron, steel, copper or brass. Consequently, the invention is based upon the unexpected differences found between these acids in a new environment which is substantially difierent from any environment in which they may previously have been employed. The advantage of capric acid as suggested above rests not only in this outstanding vapor phase inhibiting performance but also in the fact that this acid is much less costly than other vapor phase corrosion inhibitors, such as amine nitrites or amine carboxylates.

The efiectiveness of capric acid is found only at temperatures between about F. and about 110 F. At higher temperatures other phenomena. must become dominant, since capric acid then is not an efiective vapor phase corrosion inhibitor, while several of the other acids referred to become at least partially effective.

The following examples emphasize the differences obtained between the use of capric acid and its homologs in a vapor phase corrosion inhibiting test designed to demonstrate relative ability of inhibition under storage conditions between about 30 F. and about 110 F., such as would be experienced in the storage of metallic articles in warehouses or other similar situations.

In this test a metal specimen is mounted in a phenolformaldehyde resin block and suspended by means of a glass tube in a glass compartment 1 and /2 inches above a platform on which filter paper impregnated with the potential inhibitor being tested. Beneath this platform, which is a screen, water is placed and the entire apparatus is put in an oven at 100 F. for 16 hours. Subsequent to this, ice water is placed in the glass tube above and in contact with the mounted metal specimen. This permits condensation of water on the exposed specimen surface. The apparatus is then observed at 2-hour intervals. The ice water is replaced every two hours in order to provide a cool and cyclic condensation surface on the face of the metal specimen while it is kept in the 100 F. oven. The data given below demonstrate that capric acid is outstanding for ambient temperature corrosion inhibition for at least four cycles. The data also show that its close homologs, namely, caprylic acid and caproic acid were of no value, while lauric acid prevented rusting only for two cycles. The presence of methylamine caprate in combination with capric acid also provides substantially complete vapor phase corrosion inhibition.

In the above tests 4 grams of the acid were dissolved in 20 cc. of isopropyl alcohol. One-half a cc. of this solution was deposited on a filter paper of 2% inches in diameter.

It is preferred that the amount of capric acid utilized in accordance with this invention be sufiicient for a substantial period of corrosion inhibition of the particular metal being protected and under the environment to which it will be subjected. Normally, this will be an amount of capric acid between about 0.05 gram and 5 grams per square foot of the wrapping material.

I claim as my invention:

1. In a process for the vapor phase corrosion inhibition of metallic surfaces at temperatures between about 30" F. and about F. in the presence of water vapor, wherein a metallic object is enclosed in a wrapping material, the improvement which comprises enclosing a corrosioninhibiting amount of capric acid as the sole vapor phase corrosion inhibitor with the metallic object for a period of at least 8 hours.

2. The process of vapor phase corrosion inhibition which comprises enclosing an object having a metallic surface in a wrapping material together with a corrosioninhibiting amount of capric acid as the sole vapor phase corrosion inhibitor and maintaining the temperature of the wrapped object at between about 30 F. and about 110 F. in the presence of water vapor for a period of at least 8 hours.

3. A process according to claim 2, wherein the metallic surface is ferruginous and the wrapping material is paper. v 4. A process according to claim 2, wherein the capric acid is utilized in an amount between about 0.05 and about 5 grams per square foot of wrapping material.

OTHER REFERENCES Baker: Volatile Rust Inhibitors, Naval Research Laboratory Report, 4319, March 10, 1954. 

1. IN A PROCESS FOR THE VAPOR PHASE CORROSION INHIBITION OF METALLIC SURFACES AT TEMPERATURES BETWEEN ABOUT 30*F. AND ABOUT 110*F. IN THE PRESENCE OF WATER VAPOR, WHEREIN A METALLIC OBJECT IS ENCLOSED IN A WRAPPING MATERIAL, THE IMPROVEMENT WHICH COMPRISES ENCLOSING A CORROSIONINHIBITING AMOUNT OF CAPRIC ACID AS THE SOLE VAPOR PHASE CORROSION INHIBITOR WITH THE METALLIC OBJECT FOR A PERIOD OF AT LEAST 8 HOURS. 